NPC1L1 and ABCG5/8 induction explain synergistic fecal cholesterol excretion in ob/ob mice co-treated with PPAR-α and LXR agonists

Butylparaben induces glycolipid metabolic disorders in mice via disruption of gut microbiota and FXR signaling

Butylparaben, a common preservative, is widely used in food, pharmaceuticals and personal care products. Epidemiological studies have revealed the close relationship between butylparaben and diabetes; however the mechanisms of action remain unclear. In this study, we administered butylparaben orally to mice and observed that exposure to butylparaben induced glucose intolerance and hyperlipidemia. RNA sequencing results demonstrated that the enrichment of differentially expressed genes was associated with lipid metabolism, bile acid metabolism, and inflammatory response. Western blot results further validated that butylparaben promoted hepatic lipogenesis, inflammation, gluconeogenesis, and insulin resistance through the inhibition of the farnesoid X receptor (FXR) pathway. The FXR agonists alleviated the butylparaben-induced metabolic disorders. Moreover, 16 S rRNA sequencing showed that butylparaben reduced the abundance of Bacteroidetes, S24-7, Lactobacillus, and Streptococcus, and elevated the Firmicutes/Bacteroidetes ratio. The gut microbiota dysbiosis caused by butylparaben led to decreased bile acids (BAs) production and increased inflammatory response, which further induced hepatic glycolipid metabolic disorders. Our results also demonstrated that probiotics attenuated butylparaben-induced disturbances of the gut microbiota and hepatic metabolism. Taken collectively, the findings reveal that butylparaben induced gut microbiota dysbiosis and decreased BAs production, which further inhibited FXR signaling, ultimately contributing to glycolipid metabolic disorders in the liver.

Exserolide J ameliorates lipid accumulation in vitro by regulating liver X receptor alpha and peroxisome proliferator-activated receptor alpha proteins

Exserolides are isocoumarin derivatives containing lactone moiety. Recently, some isocoumarins have been demonstrated to ameliorate hyperlipidemia, a major factor for inducing cardiovascular diseases. However, the effects and mechanisms of action of exserolides on hyperlipidemia are not known. The aim of this study is to investigate whether the marine fungus Setosphaeria sp.-derived exserolides (compounds I, J, E, and F) exert lipid-lowering effects via improving reverse cholesterol transport (RCT) in vitro. RAW264.7 macrophages and HepG2 cells were used to establish lipid-laden models, and the levels of intracellular lipids and RCT-related proteins were determined by assay kits and Western blotting, respectively. We observed that exserolides (at a 5 μM concentration) significantly decreased intracellular cholesterol and triglyceride levels in oxidized low-density lipoprotein-laden RAW264.7 cells and markedly improved [3H]-cholesterol efflux. Among the four tested compounds, exserolide J increased the protein levels of ATP-binding cassette transporter A1, peroxisome proliferator-activated receptor α (PPARα), and liver X receptor α (LXRα). Furthermore, treatment with exserolides significantly decreased oleic acid-laden lipid accumulation in HepG2 hepatocytes. Mechanistically, exserolides enhance PPARα protein levels; furthermore, compound J increases cholesterol 7 alpha-hydroxylase A1 and LXRα protein levels. Molecular docking revealed that exserolides, particularly compound J, can interact with PPARα and LXRα proteins. These data suggest that the terminal carboxyl group of compound J plays a key role in lowering lipid levels by stimulating LXRα and PPARα proteins. In conclusion, compound J exhibits powerful lipid-lowering effects in vitro. However, its hypolipidemic effects in vivo should be investigated in the future.

Inhibition of PCSK9 prevents and alleviates cholesterol gallstones through PPARα-mediated CYP7A1 activation

BACKGROUND & AIMS

Dysregulated cholesterol metabolism is the major factor responsible for cholesterol gallstones (CGS). Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a critical role in cholesterol homeostasis and its inhibitors secure approval for treating various cholesterol metabolic disorders such as hypercholesterolemia and cardiovascular diseases, but its role in CGS remains unclear. Our study aims to clarify mechanisms by which PCSK9 promotes CGS formation and explore the application of the PCSK9 inhibitor, alirocumab, in preventing and treating CGS.

APPROACH & RESULTS

The expressions of PCSK9 were notably increased in CGS patients' serum, bile, and liver tissues compared to those without gallstones. Moreover, among CGS patients, hepatic PCSK9 was positively correlated with hepatic cholesterol and negatively correlated with hepatic bile acids (BAs), suggesting PCSK9 was involved in disrupted hepatic cholesterol metabolism related to CGS. Mechanistically, in vitro experiments demonstrated that inhibition of PCSK9 enhanced nuclear expression of PPARα by diminishing its lysosomal degradation and subsequently activated CYP7A1 transcription. Finally, inhibition of PCSK9 prevented CGS formation and dissolved the existing stones in CGS mice by elevating the conversion of cholesterol into BAs through PPARα-mediated CYP7A1 activation. Additionally, serum PCSK9 level may function as a prognostic signature to evaluate the therapeutic efficacy of PCSK9 inhibitors.

CONCLUSIONS

Inhibition of PCSK9 exerts preventive and therapeutic effects on CGS by activating PPARα-mediated CYP7A1 expression and facilitating the conversion of cholesterol into BAs, which highlights the potential of PCSK9 inhibition as a promising candidate for preventing and treating CGS in clinical applications.

IMPACT AND IMPLICATIONS

PCSK9 plays a pivotal role in cholesterol metabolism and its inhibitors are approved for clinical use in cardiovascular diseases. Our study observes inhibition of PCSK9 prevents and dissolves CGS by activating PPARα-mediated CYP7A1 expression and facilitating the conversion of cholesterol into BAs. Mechanistically, PCSK9 inhibition enhanced the nuclear expression of PPARα by diminishing its lysosomal degradation and subsequently activated CYP7A1 transcription. Our study sheds light on the new function and mechanism of PCSK9 in CGS, providing a novel preventive and therapeutic target with potential clinical applications.

The roles of nuclear receptors in cholesterol metabolism and reverse cholesterol transport in nonalcoholic fatty liver disease

As the most prevalent chronic liver disease globally, NAFLD encompasses a pathological process that ranges from simple steatosis to NASH, fibrosis, cirrhosis, and HCC, closely associated with numerous extrahepatic diseases. While the initial etiology was believed to be hepatocyte injury caused by lipid toxicity from accumulated triglycerides, recent studies suggest that an imbalance of cholesterol homeostasis is of greater significance. The role of nuclear receptors in regulating liver cholesterol homeostasis has been demonstrated to be crucial. This review summarizes the roles and regulatory mechanisms of nuclear receptors in the 3 main aspects of cholesterol production, excretion, and storage in the liver, as well as their cross talk in reverse cholesterol transport. It is hoped that this review will offer new insights and theoretical foundations for the study of the pathogenesis and progression of NAFLD and provide new research directions for extrahepatic diseases associated with NAFLD.

Danggui Shaoyao San ameliorates the lipid metabolism via the PPAR signaling pathway in a Danio rerio (zebrafish) model of hyperlipidemia

The escalating prevalence of hyperlipidemia has a profound impact on individuals' daily physiological well-being. The traditional Chinese medicine (TCM) prescription Danggui Shaoyao San (DSS) has demonstrated significant clinical efficacy and promising prospects for clinical application. Leveraging network pharmacology and bioinformatics, we hypothesize that DSS can ameliorate lipid metabolic disorders in hyperlipidemia by modulating the PPAR signaling pathway. In this study, we employed a zebrafish model to investigate the impact of DSS on lipid metabolism in hyperlipidemia. Body weight alterations were monitored by pre- and postmodeling weight measurements. Behavioral assessments and quantification of liver biochemical markers were conducted using relevant assay kits. Pathways associated with lipid metabolism were identified through network pharmacology and GEO analysis, while PCR was utilized to assess genes linked to lipid metabolism. Western blotting was employed to analyze protein expression levels, and liver tissue underwent Oil Red O and immunofluorescence staining to evaluate liver lipid deposition. Our findings demonstrate that DSS effectively impedes weight gain and reduces liver lipid accumulation in zebrafish models with elevated lipid levels. The therapeutic effects of DSS on lipid metabolism are mediated through its modulation of the PPAR signaling pathway, resulting in a significant reduction in lipid accumulation within the body and alleviation of certain hyperlipidemia-associated symptoms.

Conferring liver selectivity to a thyromimetic using a novel nanoparticle increases therapeutic efficacy in a diet-induced obesity animal model

Optimization of metabolic regulation is a promising solution for many pathologies, including obesity, dyslipidemia, type 2 diabetes, and inflammatory liver disease. Synthetic thyroid hormone mimics-based regulation of metabolic balance in the liver showed promise but was hampered by the low biocompatibility and harmful effects on the extrahepatic axis. In this work, we show that specifically directing the thyromimetic to the liver utilizing a nanogel-based carrier substantially increased therapeutic efficacy in a diet-induced obesity mouse model, evidenced by the near-complete reversal of body weight gain, liver weight and inflammation, and cholesterol levels with no alteration in the thyroxine (T4) / thyroid stimulating hormone (TSH) axis. Mechanistically, the drug acts by binding to thyroid hormone receptor β (TRβ), a ligand-inducible transcription factor that interacts with thyroid hormone response elements and modulates target gene expression. The reverse cholesterol transport (RCT) pathway is specifically implicated in the observed therapeutic effect. Overall, the study demonstrates a unique approach to restoring metabolic regulation impacting obesity and related metabolic dysfunctions.

Dietary diosgenin transcriptionally down-regulated intestinal NPC1L1 expression to prevent cholesterol gallstone formation in mice

BACKGROUND

Cholesterol gallstone disease is a common disease. Reducing cholesterol burden is important to prevent/treat gallstone. In this study, we investigated the application of diosgenin (DG) to prevent the formation of gallstone in mice.

METHODS

Adult male C57BL/6J mice were fed with the lithogenic diet (LD) only or LD supplemented with DG or ezetimibe for 8 weeks. Incidences of gallstone formation were documented. Intestine and liver tissues were collected to measure the lipid contents and expression of genes in cholesterol metabolism. Caco2 cells were treated with DG to monitor the regulation on cholesterol absorption and the transcriptional regulation of Npc1l1 gene. Changes of gut microbiota by DG was analyzed. Intraperitoneal injection of LPS on mice was performed to verify its effects on STAT3 activation and Npc1l1 expression in the small intestine.

RESULTS

LD led to 100% formation of gallstones in mice. In comparison, dietary DG or ezetimibe supplementary completely prevents gallstones formation. DG inhibited intestinal cholesterol absorption in mice as well as in Caco2 cells by down-regulation of Npc1l1 expression. DG could directly inhibit phosphorylation of STAT3 and its transcriptional regulation of Npc1l1 expression. Furthermore, DG could modulate gut microbiota profiles and LPS mediated STAT3 activation and Npc1l1 expression.

CONCLUSION

Our results demonstrated that dietary DG could inhibit intestinal cholesterol absorption through decreasing NPC1L1 expression to prevent cholesterol gallstone formation.

A Review of Progress on Targeting LDL Receptor-Dependent and -Independent Pathways for the Treatment of Hypercholesterolemia, a Major Risk Factor of ASCVD

Since the discovery of the LDL receptor in 1973 by Brown and Goldstein as a causative protein in hypercholesterolemia, tremendous amounts of effort have gone into finding ways to manage high LDL cholesterol in familial hypercholesterolemic (HoFH and HeFH) individuals with loss-of-function mutations in the LDL receptor (LDLR) gene. Statins proved to be the first blockbuster drug, helping both HoFH and HeFH individuals by inhibiting the cholesterol synthesis pathway rate-limiting enzyme HMG-CoA reductase and inducing the LDL receptor. However, statins could not achieve the therapeutic goal of LDL. Other therapies targeting LDLR include PCSK9, which lowers LDLR by promoting LDLR degradation. Inducible degrader of LDLR (IDOL) also controls the LDLR protein, but an IDOL-based therapy is yet to be developed. Among the LDLR-independent pathways, such as angiopoietin-like 3 (ANGPTL3), apolipoprotein (apo) B, apoC-III and CETP, only ANGPTL3 offers the advantage of treating both HoFH and HeFH patients and showing relatively better preclinical and clinical efficacy in animal models and hypercholesterolemic individuals, respectively. While loss-of-LDLR-function mutations have been known for decades, gain-of-LDLR-function mutations have recently been identified in some individuals. The new information on gain of LDLR function, together with CRISPR-Cas9 genome/base editing technology to target LDLR and ANGPTL3, offers promise to HoFH and HeFH individuals who are at a higher risk of developing atherosclerotic cardiovascular disease (ASCVD).

Macrophage inhibitory cytokine-1 aggravates diet-induced gallstone formation via increased ABCG5/ABCG8 expression

Macrophage inhibitory cytokine 1 (MIC-1), which is overproduced in various human cancers and associated with cachexia, acts on the hypothalamus to suppress appetite and reduce body weight. We investigated the mechanisms through which MIC-1 affects bile acid metabolism and gallstone formation, which are poorly understood. Over 6 weeks, male C57BL/6 mice fed either standard chow or a lithogenic diet were intraperitoneally injected with phosphate-buffered saline (PBS) or MIC-1 (200 μg/kg/week). Among lithogenic diet-fed mice, MIC-1 treatment resulted in increased gallstone formation compared with PBS treatment. Compared with PBS treatment, MIC-1 treatment decreased hepatic cholesterol and bile acid levels and reduced expression of HMG-CoA reductase (HMGCR), the master cholesterol metabolism regulator sterol regulatory element-binding protein 2, cholesterol 7α-hydroxylase (CYP7A1), mitochondrial sterol 27-hydroxylase, and oxysterol 7α-hydroxylase. Compared with PBS treatment, MIC-1 treatment had no effect on small heterodimer partner, farnesoid X receptor, or pregnane X receptor expression, and extracellular signal-related kinase and c-Jun N-terminal kinase phosphorylation decreased, suggesting that these factors do not contribute to the MIC-1-induced reduction in CYP7A1 expression. Compared with PBS treatment, MIC-1 treatment increased AMP-activated protein kinase (AMPK) phosphorylation. Treatment with the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) reduced CYP7A1 and HMGCR expression, whereas the AMPK inhibitor Compound C reversed MIC-1-induced reductions in CYP7A1 and HMGCR expression. Furthermore, in MIC-1-treated mice, total biliary cholesterol levels increased together with increased ATP-binding cassette subfamily G (ABCG)5 and ABCG8 expression. Compared with PBS treatment, MIC-1 treatment did not affect expression of liver X receptors α and β, liver receptor homolog 1, hepatocyte nuclear factor 4α, or NR1I3 (also known as constitutive androstane receptor), which are upstream of ABCG5/8; however, MIC-1 treatment increased ABCG5/8 expression and promoter activities. Our study indicates that MIC-1 influences gallstone formation by increasing AMPK phosphorylation, reducing CYP7A1 and HMGCR expression, and increasing ABCG5 and ABCG8 expression.

The Hypolipidemic Effect of Hawthorn Leaf Flavonoids through Modulating Lipid Metabolism and Gut Microbiota in Hyperlipidemic Rats

Objective. The purpose of this study was to explore the potential mechanisms of the lipid-regulating effects and the effect on modulating the gut microbiota of hawthorn leaf flavonoids (HLF) in the high-fat diet-induced hyperlipidemic rats. Methods. The hypolipidemic effect of HLF was investigated in the high-fat diet-induced hyperlipidemic rats. The action targets of HLF in the treatment of hyperlipidemia were predicted by network pharmacology and KEGG enrichment bubble diagram, which were verified by the test of western blotting. Meanwhile, we used 16S rRNA sequencing to evaluate the effects of HLF on the microbes. Results. The results of animal experiments showed that HLF could reduce the body weight and regulate the levels of serum lipid in high-fat diet (HFD) rats. Meanwhile, for the related targets of cholesterol metabolism, HLF could significantly upregulate the expression of LDLR, NR1H3, and ABCG5/ABCG8; reduce the expression of PCSK9; and increase the level of CYP7A1 in the intestinal tissue, whereas cholesterol biosynthetic protein expressions including HMGCR and SCAP were lowered by HLF. In addition, HLF increased the activities of plasma SOD, CAT, and GSH-Px and decreased the levels of Casp 1, NLRP3, IL-1β, IL-18, and TNF-α, improving the degree of hepatocyte steatosis and inflammatory infiltration of rats. Notably, HLF significantly regulated the relative abundance of major bacteria such as g_Lactobacillus, g_Anaerostipes, g_[Eubacterium]_hallii_group, g_Fusicatenibacter, g_Akkermansia, and g_Collinsella. Synchronously, we found that HLF could regulate the disorder of plasma HEPC and TFR levels caused by HFD. Conclusion. This study demonstrates that HLF can regulate metabolic hyperlipidemia syndromes and modulate the relative abundance of major bacteria, which illustrated that it might be associated with the modulation of gut microbiota composition and metabolites.

The role of exercise intensity on fatty liver in rats

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and is often caused by obesity. Currently, moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) are two effective treatments for reducing fat mass in patients with obesity and NAFLD. However, the comparative fat-reducing effects and underlying molecular mechanisms of MICT and HIIT remain unclear. This comprehensive study was performed on male Wistar rats treated with standard diet, high-fat diet, MICT, and HIIT to explore their comparative fat-reducing effects and corresponding molecular mechanisms. HIIT had a greater effect on hepatic vacuolation density and lipid content reduction than MICT, and triglyceride and total cholesterol levels in the serum and the liver demonstrated different sensitivities to different exercise training programs. At the molecular level, both MICT and HIIT altered the processes of fatty acid synthesis, fatty acid transport, fatty acid β-oxidation, and cholesterol synthesis, wherein the transcriptional and translational levels of signaling molecules peroxisome proliferator-activated receptors (PPARs) regulating fatty acid and cholesterol synthesis were strongly changed. Moreover, the metabolic pathways of amino acids, bile acids, and carbohydrates were also affected according to transcriptome analysis, and the changes in the above-mentioned processes in the HIIT group were greater than those in the MICT group. In combination with the search tool for the retrieval of interacting genes/proteins (STRING) analysis and the role of PPARs in lipid metabolism, as well as the expression pattern of PPARs in the MICT and HIIT groups, the MICT-and HIIT-induced fat loss was mediated by the PPAR pathway, causing feedback responses in fatty acid, steroid, amino acid, bile acid, and carbohydrate metabolism, and HIIT had a better fat-reducing effect, which may be initiated by PPAR-α. This study provides a theoretical basis for targeted therapy of patients with obesity and NAFLD.

Sterol carrier protein 2 in lipid metabolism and non-alcoholic fatty liver disease: Pathophysiology, molecular biology, and potential clinical implications

Non-alcoholic fatty liver disease (NAFLD) is considered as the most common chronic liver disease and has become a rapidly global public health problem. Sterol carrier protein 2 (SCP-2), also called non-specific lipid-transfer protein, is predominantly expressed by the liver. SCP-2 plays a key role in intracellular lipid transport and metabolism. SCP-2 has been closely implicated in the development of NAFLD-related metabolic disorders, such as obesity, atherosclerosis, Type 2 diabetes mellitus (T2DM), and gallstones. Recent studies indicate that SCP-2 plays a beneficial role in NAFLD by regulating cholesterol-, endocannabinoid-, and fatty acid-related aspects of lipid metabolism. Hence, in this paper, we summarize the latest findings about the roles of SCP-2 in hepatic steatosis and further describe its molecular function in the pathogenesis of NAFLD.

HDL as Bidirectional Lipid Vectors: Time for New Paradigms

The anti-atherogenic properties of high-density lipoproteins (HDL) have been explained mainly by reverse cholesterol transport (RCT) from peripheral tissues to the liver. The RCT seems to agree with most of the negative epidemiological correlations between HDL cholesterol levels and coronary artery disease. However, therapies designed to increase HDL cholesterol failed to reduce cardiovascular risk, despite their capacity to improve cholesterol efflux, the first stage of RCT. Therefore, the cardioprotective role of HDL may not be explained by RCT, and it is time for new paradigms about the physiological function of these lipoproteins. It should be considered that the main HDL apolipoprotein, apo AI, has been highly conserved throughout evolution. Consequently, these lipoproteins play an essential physiological role beyond their capacity to protect against atherosclerosis. We propose HDL as bidirectional lipid vectors carrying lipids from and to tissues according to their local context. Lipid influx mediated by HDL appears to be particularly important for tissue repair right on site where the damage occurs, including arteries during the first stages of atherosclerosis. In contrast, the HDL-lipid efflux is relevant for secretory cells where the fusion of intracellular vesicles drastically enlarges the cytoplasmic membrane with the potential consequence of impairment of cell function. In such circumstances, HDL could deliver some functional lipids and pick up not only cholesterol but an integral part of the membrane in excess, restoring the viability of the secretory cells. This hypothesis is congruent with the beneficial effects of HDL against atherosclerosis as well as with their capacity to induce insulin secretion and merits experimental exploration.

Beneficial Effect of Fenofibrate and Silymarin on Hepatic Steatosis and Gene Expression of Lipogenic and Cytochrome P450 Enzymes in Non-Obese Hereditary Hypertriglyceridemic Rats

The efficacy of fenofibrate in the treatment of hepatic steatosis has not been clearly demonstrated. In this study, we investigated the effects of fenofibrate and silymarin, administered as monotherapy and in combination to existing hepatic steatosis in a unique strain of hereditary hypertriglyceridemic rats (HHTg), a non-obese model of metabolic syndrome. HHTg rats were fed a standard diet without or with fenofibrate (100 mg/kg b.wt./day) or with silymarin (1%) or with a combination of fenofibrate with silymarin for four weeks. Fenofibrate alone and in combination with silymarin decreased serum and liver triglycerides and cholesterol and increased HDL cholesterol. These effects were associated with the decreased gene expression of enzymes involved in lipid synthesis and transport, while enzymes of lipid conversion were upregulated. The combination treatment had a beneficial effect on the gene expression of hepatic cytochrome P450 (CYP) enzymes. The expression of the CYP2E1 enzyme, which is source of hepatic reactive oxygen species, was reduced. In addition, fenofibrate-induced increased CYP4A1 expression was decreased, suggesting a reduction in the pro-inflammatory effects of fenofibrate. These results show high efficacy and mechanisms of action of the combination of fenofibrate with silymarin in treating hepatic steatosis and indicate the possibility of protection against disorders in which oxidative stress and inflammation are involved.

Regulation of the expression of cholesterol transporters by lipid-lowering drugs ezetimibe and pemafibrate in rat liver and intestine

Ezetimibe and pemafibrate are lipid-lowering drugs and promote reverse cholesterol transport. However, it is unknown whether cholesterol is mainly excreted by hepatobiliary excretion or by non-biliary transintestinal cholesterol efflux (TICE). We evaluated the effects of ezetimibe and pemafibrate on hepatic and intestinal cholesterol transporter regulation in Sham-operated rats, and examined the effects of these drugs on TICE in bile duct-ligated rats. Seven-week-old male Sprague-Dawley rats were treated as follows for two weeks: 1) Sham, Sham operation; 2) BDL, bile duct ligation; 3) E-Sham, Sham + ezetimibe; 4) E-BDL, BDL + ezetimibe; 5) P-Sham, Sham + pemafibrate; and 6) P-BDL, BDL + pemafibrate. Blood, liver, jejunum, and feces were collected 72 h post-surgery. Hepatic cholesterol levels were decreased in P-Sham and E-Sham, and were lower in E-BDL and P-BDL than in BDL. Fecal cholesterol levels increased in E-Sham and P-Sham compared with Sham, and were higher in E-BDL and P-BDL than in BDL. In liver, Abcg5 mRNA showed induction in E-Sham, Abcg5 and Abca1 mRNA were induced in P-Sham, Abcg5 mRNA was reduced in E-BDL, and Abca1 mRNA was increased in P-BDL. In jejunum, Abcg5 mRNA was induced in E-Sham. Abcg8 mRNA was induced in E-Sham and P-Sham. NPC1L1 mRNA showed reduced expression in P-Sham and P-BDL. SR-B1 mRNA was reduced in P-Sham, and the expression decreased in P-BDL. LDL receptor mRNA was induced in BDL and P-BDL. Ezetimibe and pemafibrate may promote TICE by increasing Abcg5/g8, while pemafibrate may inhibit intestinal cholesterol absorption by decreasing SR-B1 and NPC1L1.